Which one among the following is an example of oxidation reaction ?

Freezing of water

Dissolving sugar in water

Rusting of iron

Boiling of petrol

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UPSC NDA-2 – 2024

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Oxidation is a chemical reaction where a substance loses electrons or its oxidation state increases. Rusting of iron is the process where iron reacts with oxygen and water to form hydrated iron(III) oxides, commonly known as rust. This is a chemical change where iron is oxidized from its elemental state (oxidation state 0) to an oxidation state of +3 in the iron oxides. Freezing of water, dissolving sugar, and boiling of petrol are physical changes or processes, not chemical reactions involving oxidation in the typical sense tested in such questions.

An oxidation reaction involves the loss of electrons or an increase in oxidation state. Chemical changes result in the formation of new substances. Physical changes alter the form or appearance but not the chemical composition.

Rusting is a specific type of corrosion, which is an electrochemical process. The chemical equation for the formation of rust is complex, but the overall process involves the oxidation of iron: Fe → Fe³⁺ + 3e⁻, and the reduction of oxygen.

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